Kneecap Dislocation Surgery: When Is MPFL Reconstruction Needed?

Key Takeaways

• A first kneecap dislocation is usually managed without surgery, with reduction, imaging and structured rehabilitation.
• Reconstruction is typically considered when dislocations repeat, a loose fragment is found, or the knee still feels unsafe despite good rehabilitation.
• Bone shape and alignment influence the plan, so some knees may need a tibial tubercle osteotomy or trochleoplasty alongside ligament surgery.
• Walking often normalises within two to four weeks, while return to pivoting sport commonly takes closer to nine to 12 months.

The kneecap slides sideways, the leg gives way, and the ground arrives sooner than expected. Sometimes it slips back on its own the moment the leg straightens. Sometimes it is still sitting on the outside of the knee when help arrives. The same question surfaces within a week or two. Is kneecap dislocation surgery something you will need, or can this settle with rehabilitation alone?

The answer is rarely decided by a single scan. Most first dislocations are treated without surgery. What changes the conversation is what the knee does next, what imaging shows about the shape of the joint, and how much the fear of another episode is limiting you.

Surgery to rebuild the medial patellofemoral ligament (MPFL) has become a common way to stabilise a kneecap that keeps letting go. Understanding when MPFL reconstruction surgery is appropriate, and when it is not, helps you weigh up the options with your treating team.

What Happens When Your Kneecap Dislocates

A dislocation does more than move a bone out of place for a few painful seconds. What failed, and what was damaged on the way back in, both shape what comes next:

The Groove That Holds the Patella in Place

The kneecap, or patella, glides in a shallow channel at the end of the thigh bone known as the trochlear groove. Once the knee bends past roughly 30 degrees, bone shape does most of the stabilising work. Near full extension, the kneecap sits above the deepest part of the channel and relies far more on soft tissue to stay centred. That early range is where most dislocations happen.

The Role of the Medial Patellofemoral Ligament

The MPFL runs from the inner border of the kneecap to the inner side of the thigh bone, working as the main checkrein against the patella sliding outwards through that vulnerable early range. It is a small structure, and it is not built to resist repeated force on its own.

The Damage a Dislocation Leaves Behind

When the patella jumps the outer wall of the groove, the MPFL stretches or tears in almost every case. As the kneecap relocates, it strikes the outer edge of the thigh bone, which can bruise bone and shear off a fragment of cartilage or bone. Bleeding fills the joint, swelling arrives quickly, and the quadriceps often switches off within hours.

The Difference Between Dislocation and Subluxation

A full dislocation means the kneecap leaves the groove completely and usually needs to be guided back. A subluxation means it slides partway out and returns on its own. Both load the same ligament and both can leave a knee that feels unreliable, which is why near-misses are worth mentioning to your clinician.

Why Some Kneecaps Keep Slipping Out

Recurrence is rarely bad luck. Most people who dislocate more than once carry at least one feature that makes the patella harder to hold in place:

Shallow Trochlear Groove

A groove that is flat, or in some cases slightly domed, gives the kneecap far less to sit in. This is known as trochlear dysplasia, and it is one of the stronger predictors of repeat instability. It is present from early life and shows up on X-ray, magnetic resonance imaging (MRI) or computed tomography (CT).

High-Riding Kneecap

Patella alta describes a kneecap sitting higher than usual relative to the joint. It enters the groove later in the bend, which leaves a longer window where soft tissue is doing the work alone.

Wide Tibial Tubercle to Trochlear Groove Distance

The patellar tendon anchors onto a bump on the shin called the tibial tubercle. When that anchor point sits further out than average, the pull on the kneecap angles outwards. Surgeons measure this as the tibial tubercle to trochlear groove (TT-TG) distance on CT or MRI.

Generalised Ligament Laxity

Some people have naturally stretchy connective tissue across many joints. Increased laxity may mean the MPFL is less able to resist force, and it can influence how a graft behaves after surgery.

Limited Hip and Quadriceps Control

Weakness through the hip and quadriceps allows the knee to fall inwards during landing, pivoting and stair descent, which drives the kneecap towards the outer wall. Unlike bone shape, this factor responds directly to training.

Younger Age and Earlier Episodes

Kneecap dislocation is far more common during adolescence, with reported rates of around 29 per 100,000 in people under 18 compared with roughly 5.8 per 100,000 in adults. Each further episode also raises the likelihood of the next one.

What Usually Happens After a First Kneecap Dislocation

The days and weeks after a first dislocation follow a consistent sequence:

Restoring Kneecap Position

Trying to force a dislocated patella back yourself risks further damage. Many relocate as the leg is gently straightened, often before help arrives. When it stays out, reduction is performed by a clinician, sometimes with pain relief or sedation in an emergency department.

Confirming Injury With Imaging

X-rays are usually taken to look for fractures and loose fragments. An MRI may follow to assess the MPFL, the cartilage surfaces and any bone bruising. CT is sometimes added when alignment and TT-TG distance need measuring. Imaging is also where high-risk anatomy is first identified.

Settling Swelling and Stiffness

A brace or splint may be used briefly for comfort and confidence, though prolonged immobilisation is generally avoided. Early priorities are reducing swelling, regaining full straightening and switching the quadriceps back on.

Rebuilding Strength and Control

Progressive loading targets the quadriceps, the hip abductors and rotators, and trunk control, with balance and landing work added as the knee tolerates it. This phase typically runs over several months and rebuilds confidence as well as strength.

Returning to Sport in Stages

Return is guided by strength, hop and control testing alongside symptoms. Even with good rehabilitation, recurrent instability after a first dislocation is commonly reported in around 30% of cases, and higher again in younger patients with high-risk anatomy.

When MPFL Reconstruction Is Usually Considered

No single finding decides this. An orthopaedic surgeon’s assessment weighs how often the kneecap has given way, what the instability is costing you, and what imaging shows about why it keeps happening. Several situations move the discussion towards reconstruction:

Recurrent Dislocations Despite Rehabilitation

Repeated dislocation is usually the clearest indication. Once instability is established, further rehabilitation on its own is less likely to change the pattern, and every episode carries a risk of new cartilage damage.

Ongoing Apprehension in Everyday Movement

Some knees never dislocate again but never feel safe either. Avoiding stairs, refusing to turn quickly or bracing before every step is a functional problem worth raising even without a second episode.

Loose Fragments Inside the Joint

A displaced piece of bone and cartilage may need fixing or removing regardless of the instability, and this is one of the few reasons early surgery may be considered after a first dislocation. Stabilisation is often performed at the same time.

High-Risk Anatomy After a First Episode

A young patient with marked trochlear dysplasia, patella alta and a wide TT-TG distance carries a substantially higher recurrence risk. Some surgeons use published risk scores to frame that conversation, and earlier stabilisation may be raised as an option.

Persistent Instability at Work and Home

Kneeling trades, shift work on uneven ground or lifting small children can make an unpredictable kneecap unsafe. The threshold for surgery may sit lower when a fall carries serious consequences.

Previous Surgery Without Lasting Stability

Older approaches such as isolated lateral release do not restore the medial restraint and may leave instability unresolved. Revision planning usually starts by reassessing the anatomy from the beginning.

What MPFL Reconstruction Involves

The operation rebuilds the restraint that failed, and several details are settled only once the joint has been inspected:

Anaesthetic and Day Surgery

Surgery is commonly performed under a general anaesthetic as day surgery, often with a nerve block or local anaesthetic for comfort afterwards. It usually takes one to two hours, with extra time either side for anaesthetic and recovery.

Arthroscopy and Joint Assessment

Two or three small incisions allow a camera into the knee to check cartilage surfaces, kneecap tracking and any damage from previous episodes.

Graft Choice and Preparation

The graft may be synthetic or taken from one of your own hamstring tendons, in which case a small incision is made on the inner shin. Graft choice depends on age, tissue quality, activity level and surgeon preference.

Graft Placement and Tensioning

The graft is passed along the line of the original ligament and fixed to the inner edge of the kneecap and to the thigh bone using anchors, screws, sutures or buttons. Tension is checked carefully, because a graft set too tight can increase pressure behind the kneecap.

When the Ligament Alone Is Not Enough

Rebuilding the MPFL restores the soft tissue restraint. It does not change the shape of the groove or the direction the tendon pulls, so some knees need more:

Tibial Tubercle Osteotomy

Moving the bony attachment of the patellar tendon changes the direction of pull on the kneecap and can shift load away from damaged cartilage. This may be considered when TT-TG distance is high or the patella sits too high. Weight-bearing may be restricted for six weeks or more afterwards, which extends the return-to-sport timeline.

Trochlear Groove Reshaping

A trochleoplasty reshapes a severely flat or domed groove and is reserved for selected cases, because it is a more involved procedure carrying its own risks and a longer recovery.

Cartilage Surface Repair

Damage to the joint surface behind the kneecap may need treatment in its own right. Addressing instability without addressing cartilage can leave pain behind once stability improves.

Lateral Soft Tissue Lengthening

Tight tissue on the outer side of the kneecap may be lengthened when it contributes to tilt. Used on its own, it is generally not enough to control instability.

Recovery and Return to Sport After MPFL Reconstruction

Early recovery after an isolated ligament reconstruction is often quicker than people expect, while full return to pivoting sport takes considerably longer. Progress is measured by capability, not by dates:

Managing Swelling and Weight-Bearing

Crutches are usually provided, and many people can put weight through the leg soon after an isolated reconstruction. Swelling control, wound care and gentle movement dominate the first fortnight. A brace may be used when additional procedures were performed.

Restoring Movement and Quadriceps Strength

Walking commonly normalises within two to four weeks. From around six weeks, strengthening becomes the focus, with cycling, controlled squatting patterns and work on how the kneecap tracks through the bend.

Building Single-Leg Control and Confidence

Between three and six months, attention shifts to single-leg strength, landing mechanics and change of direction, following the same staged pattern as an anterior cruciate ligament (ACL) recovery timeline.

Testing Strength and Readiness

Strength testing, hop testing and movement quality assessments help decide when pivoting sport is reasonable. Full return often sits closer to nine to 12 months, and going back early raises the risk of graft failure or another dislocation.

Returning to Work and Driving

Office work is often possible within one to two weeks. Heavy manual work may take two to three months, particularly where ladders, kneeling or uneven ground are involved. Driving usually requires around two weeks for a left knee in an automatic vehicle and at least six weeks for a right knee, provided an emergency stop can be performed safely and stronger pain relief has stopped.

These timeframes are a general guide only. Your own recovery may differ depending on the procedures performed, your starting strength and how the knee responds.

Costs, Medicare and Cover in Australia

What you pay depends on where the surgery happens, what cover you hold and how many procedures are performed together:

Medicare Items and Schedule Fees

Stabilisation of the patellofemoral joint by combined open and arthroscopic means is billed under Medicare Benefits Schedule item 49564. The schedule fee was $1,100.10 as at 1 July 2026, with Medicare paying 75% for admitted private patients and your fund generally covering at least the remainder where the procedure is included on your policy. Item 49565 covers the more complex reconstruction that combines medial soft tissue reconstruction with tibial tuberosity transfer, and may also include bone graft, internal fixation or trochleoplasty, with a schedule fee of $1,578.80. The schedule fee is a government benchmark and not the amount a surgeon charges.

Private Cover and Out-of-Pocket Costs

With appropriate hospital cover, Medicare and your fund each pay a share of surgeon, anaesthetist and assistant fees, and the remainder is your gap. The anaesthetist bills independently, so that quote is worth checking separately. A policy excess, commonly around $500, may also apply, and some surgeons take part in the no-gap or known-gap arrangements offered by individual funds. The same structure applies across knee ligament procedures, including ACL surgery costs.

Public Hospital Access and Waiting Times

Surgery through the public system carries no out-of-pocket surgical cost. Waiting times vary by hospital and by the urgency category assigned after specialist review, and elective stabilisation is generally not categorised as urgent.

Rehabilitation and Follow-Up Costs

Physiotherapy sessions, any bracing and follow-up imaging sit outside the surgical fee. Private health extras cover may contribute to physiotherapy, usually up to an annual limit.

Fees, benefits and thresholds listed here are a general guide only and can change. Confirm current figures with your surgeon, your health fund and Medicare before making a decision.

Questions Worth Asking at Your Consultation

Coming prepared makes the appointment more useful, particularly when the decision is finely balanced:

• What is driving the instability in my knee, beyond the torn ligament?
• What do my X-ray, MRI and CT findings show about groove shape, kneecap height and alignment?
• What is my likely risk of another dislocation without surgery?
• What are the chances that ligament reconstruction alone will be enough?
• What does recovery look like for my job, my sport and my timeframe?
• What happens if I decide to wait and see how the knee settles?

Living Without Waiting for the Next Dislocation

A kneecap that has let go once changes how you move, often more than the injury itself warrants. The hesitation on stairs and the decision to skip the game tend to outlast the swelling.

Knowing where you sit on the pathway takes much of that uncertainty away. One dislocation with settled anatomy and a strong response to rehabilitation is a different situation from three dislocations, a shallow groove and a knee that gives way on a footpath. Both are manageable, and both become clearer once your knee has been assessed properly.

The team at MTP Health can assess what is driving your kneecap instability and talk you through the options, and your general practitioner (GP) can arrange specialist review when that is the right next step.

Frequently Asked Questions (FAQs)

1. How do I know whether my kneecap dislocated or the knee simply gave way?

A dislocated kneecap usually sits visibly out of place towards the outer side of the knee, and straightening the leg is difficult until it returns. Rapid swelling and a memory of something shifting sideways both point towards a kneecap injury.

A knee that gives way without visible deformity may involve other structures, including the cruciate ligaments or the meniscus. An assessment is worthwhile either way, because the treatment pathways differ.

2. Can a dislocated kneecap heal without surgery?

Often, yes. The torn ligament heals with scar tissue, and a structured rehabilitation program can restore strength, control and function well enough for many people to return to full activity.

What non-surgical care cannot change is the shape of the groove or the height of the kneecap, which is why recurrence rates are higher in some knees than others.

3. How long should I wait before deciding about surgery?

There is rarely pressure to decide immediately unless a loose fragment needs attention. Many surgeons suggest completing a full course of rehabilitation first, often around three months, then reassessing stability, strength and confidence.

Waiting also allows swelling to settle, which makes the physical examination and any repeat imaging more informative.

4. Does MPFL reconstruction use my own tendon?

Sometimes. A hamstring tendon graft is one common option, while a synthetic graft may be used in other cases. Your surgeon will explain which is being planned and why.

Harvesting your own tendon adds a small incision on the inner shin and may cause discomfort at the donor site for a period afterwards.

5. Will reconstruction stop my kneecap pain?

The aim of the operation is stability. Many people find pain settles once the kneecap stops slipping, because the joint is no longer being repeatedly irritated.

Pain driven by cartilage damage or patellofemoral arthritis may persist even when stability improves, so it is worth clarifying expectations with your surgeon beforehand.

6. Can I play sport again after kneecap dislocation surgery?

Many people do return to sport, including change-of-direction sports, though the timeline is measured in months and clearance depends on strength, control and confidence testing.

Sports built on repeated cutting and pivoting sit at the later end of that range, and any bony procedure performed alongside the ligament reconstruction extends it further.

7. Is MPFL reconstruction suitable for adolescents who are still growing?

It can be, with modifications. Open growth plates near the ligament attachment on the thigh bone call for careful technique and imaging, and fixation may be adjusted to avoid them.

Decisions in this group usually weigh a higher recurrence risk against growth considerations.

8. What happens if the kneecap dislocates again after surgery?

Recurrence is uncommon but possible, particularly when the graft is loaded too early or when underlying bone shape was not addressed at the time.

Reassessment usually includes fresh imaging and a review of whether alignment, groove shape or cartilage now needs treating alongside a revision.

9. Do I need a referral to see a surgeon about kneecap instability?

A referral from a GP or another specialist is generally required for a Medicare rebate on a specialist consultation.

Your physiotherapist can also flag when a surgical opinion is worth arranging, particularly when instability persists despite consistent rehabilitation.

This article is general information only and does not take your personal circumstances, medical history or diagnosis into account. It is not a substitute for individual advice, and it does not create a practitioner and patient relationship. All surgery carries risk and outcomes vary between individuals. Speak with a qualified health practitioner, such as your GP, physiotherapist or orthopaedic surgeon, before making decisions about your knee.